Springs are mechanical components in very widespread use. They are generally made of metal, which poses problems when the equipment in which the springs are incorporated is used at a temperature that is very high or in a medium that is very aggressive.
In order to solve those problems, it is reasonable to propose replacing the metal constituting a spring with a material that is capable of withstanding such operating conditions without damage, and in particular with a thermostructural composite material.
Thermostructural composite materials are characterized by their mechanical properties which make them suitable for constituting structural elements, and by their ability to conserve these properties up to temperatures that are very high.
Well-known thermostructural composite materials are carbon/carbon composite materials (C/Cs) constituted by fiber reinforcement made of carbon fibers and densified by a carbon matrix, and ceramic matrix composite materials (CMCs) constituted by fiber reinforcement made of refractory fibers, e.g. carbon fibers or ceramic fibers, and densified by a ceramic matrix.
In addition to their refractory nature, C/Cs and CMCs have the advantage of being capable of withstanding certain atmospheres that are particularly corrosive for metals.
Proposals have already been made for making springs out of C/C composite materials.
Thus, document U.S. Pat. No. 4,412,675 discloses a method consisting in preparing an organic material filled with carbon fibers, in shaping it to obtain a helical spring, and then applying heat treatment for carbonization purposes. Nevertheless, that method is limited to making helical springs and it is relatively complex in that it requires prior preparation of compounds that are suitable for being extruded so that they can be coiled.
Document EP-A-0 684 216 discloses two methods: one consisting in making a helical coil from a thread that is pre-impregnated or surrounded in a polymer sleeve, and then molded under pressure, the other consisting in making a workpiece out of C/C material and then in machining the spring from the workpiece. The first method is limited to making helical springs and requires equipment suitable for molding springs of particular shapes under pressure. The second method leads to springs of very high cost given that C/C composite materials are expensive and large amounts of material are lost in the machining.